Such a ram boring machine is described in German patent specification 23 40 751. In this ram boring machine the control sleeve passes through a guide member fixed to the housing, and during operation stops on the guide member and the control sleeve effect axial arresting. The control sleeve has a rotation arresting device that can be unlocked easily from outside: by rotating the control sleeve the stop or stops of the guide member or the control sleeve are brought into axial alignment with one or more longitudinal recesses in the control sleeve or in the guide member so that the control sleeve can be axially displaced. For reversing it is necessary first to disengage the rotation securing device, for example by tension on a cord carried with it, and then positively rotate the control sleeve relative to the guide member, then displace it and finally arrest it again.
In operation, it has been found that this ram boring machine, particularly when driven far into the ground, can only be reversed with difficulty from backward to forward movement. Thus by means of the supply hose the control sleeve must be pushed in a pressureless state the entire length of the earth bore into the forward position. This has proved difficult to do, particularly if, in the case of loose, yielding soil, the bore has partly caved in. The fact that reversing from backward to forward movement is only possible in an absolutely pressureless state is particularly disadvantageous in soils containing water, as water and dirt quickly enter the machine when it has been turned off for reversing, and the machine will then not start up again. It is a further disadvantage that a reversing cord has to be pulled along behind which can easily get caught up and can then cause unintentional reversing or can break.
Finally, it is difficult to lock or unlock the control sleeve by means of the rope-operated rotation securing device by rotating the supply hose, particularly when the earth bore is already very deep.